This invention relates to a novel heat pump system which uses low-grade energy sources such as provided by air heated by the combustion of gas, oil, exhaust gases, geothermal fluids, waste gases and solar energy which is capable of providing space heating and cooling requirements of a building.
For over forty years, residential and small commercial buildings have been cooled almost exclusively by electrically driven compressor air conditioning units. The primary reasons for this are: (1) the relatively low initial cost of the equipment; (2) a high coefficient of performance, usually two to three, which, together, with dependability and long equipment lifetime provides low operating costs; and (3) the use of aircooled condensers and evaporators which reduces the system's complexity and costs. The coefficient of performance (COP) equals refrigeration effect (Q) divided by net work input (W). This may be expressed as COP=778Q/W where "Q" is the heat in BTUs absorbed by the unit per pound refrigerant and "W" is the work in foot pounds supplied to unit, in this case its compressor.
Existing gas-fired cooling systems generally have on the other hand: (1) a low coefficient of performance, usually less than 0.7 and therefore relatively high operating costs; (2) the need for a cooling tower to serve for the purposes of the condenser which therefore increases initial and operating cost of the system; and (3) the requirement to use corrosive substances such as ammonia or lithium bromide solutions that reduce equipment lifetime and increase maintenance and operating costs.
As a result, whereas the residential market for gas is substantial in the winter and when heating is otherwise required, it is not significant in the cooing season. This contributes to poor utilization of distribution and storage capacities of the gas and liquid fuel industries as well as for the electric utilities.
With the introduction of electrically driven heat pumps which have a coefficient of performance of three to four and are capable of both heating and cooling, it can be anticipated that the efficient distribution of gas and liquid fuel from producer to consumer will be further eroded. If this is not to occur, a gas-energized cooling system must be provided which is realistically competitive with conventional existing air-conditioning systems for relatively small buildings. If such system is to comprise a gas-fired heat pump, it must have a coefficient of performance reasonably competitive with that of the electrically driven heat pump and otherwise be competitive which means that it have the same low initial equipment costs, long equipment lifetime and dependability of conventional heating and cooling systems, or better.
The coefficient of performance of gas fired cooling systems may be increased by providing two-stage absorption systems. Unfortunately, due to the complexity of such systems including the need for a cooling tower, the initial investment and operating and maintenance requirements are not as a practical matter compatible with residential and small building heating and cooling needs.
The principle of energy recycling is old and has been used in practical applications since at least the 1920's. The device employed for this purpose is usually called a regenerator and is used extensively with gas turbines in large power plants. The regenerator may be a rotor having cylindrical packing through which hot and cold gases pass simultaneously. Heat temporarily stored in such packing from the hot gas is physically moved into the cold gas stream by steadily rotating the cylindrical body which contains a checkerwork for the storage of thermal energy. A fixed two-bed regenerator system may also be used. This comprises two containers wherein reversals in the fixed bed system are effected by the closing and opening of relevant valves, shutting off the hot/cold gas and allowing the start of the flow of the cold/hot gas through the packing. With the two-bed regenerator system, one of the regenerators is, at any instant, preheating the cold gas. Regenerators are common in glass making furnaces where they must be able to withstand entrance gas temperatures on the order of 1600.degree. C. The state of the art on existing commercial devices used for the recycling of energy may be found in "Thermal Energy Storage and Regeneration" by Schmidt and Willmott, published in 1981 by Hemisphere Publishing Corporation, McGraw-Hill. Attention is also invited to U.S. Pat. No. 4,183,227 issued Jan. 15, 1980 of J. Bouvin et al.